Today's propeller aircraft generally include variable pitch propeller systems. Typically, a variable pitch propeller system for aircraft includes a plurality of propeller blades extending radially from a central hub, an engine for rotating the hub and propeller blades, and a pitch actuating system that pivots the propeller blades about their longitudinal axis to vary the angle (pitch) of the blades with respect to the approaching airflow. The pitch actuating system is hydraulically controlled by a propeller control unit (PCU) and is hydraulically powered by a PCU pump of an aircraft system.
PCU pumps are usually operatively connected to and thus driven by propeller shafts of the aircraft system. PCU pumps are conventionally unidirectional, either clockwise or counter-clockwise. The selective use of clockwise and counter-clockwise PCU pumps is determined in accordance with the propeller shafts to which the PCU pumps are to be operatively connected.
In a multi-propeller aircraft system, it has been considered to be advantageous to the aircraft system performance that the propellers of the aircraft rotate in different directions, namely some propellers rotate in a clockwise direction and the remaining propellers rotate in a counter-clockwise direction. This can be achieved by providing either a clockwise or counter-clockwise propeller gearbox to couple the particular propeller shaft to each engine which drives that propeller. In order to meet with this type of demand, aircraft engine manufacturers are required to provide both clockwise and counter-clockwise PCU pumps for a single design of aircraft system, which increases manufacturing costs due to the need for double the pump inventory.
Reversible rotary pumps have been well known and used in other industries. Those reversible rotary pumps, however, are usually relatively complicated and therefore are not suitable for application in the aircraft industry. PCU pumps for an aircraft system are required to be reliable in performance and light in weight.
Therefore, there is a need for an apparatus for driving a unidirectional PCU pump of an aircraft system which overcomes the problems in the prior art.